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Flange vs. butt welds? (LONG)

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  • Flange vs. butt welds? (LONG)

    Hey another newbie question for you. I'm gearing up to get started on my Studebaker truck project. The details are spelled out in the website link below, but here's the Reader's Digest version:

    I'm mounting a '51 Studebaker 3/4-ton pickup on an '82 Chevy Silverado CrewCab dually chassis. I'm going to have to shorten the frame about 12"-16" and I want to make an extended cab out of the Studebaker (need more room for my feet. I'd swear everyone in the '50s was only 4' tall!). I'll also be stretching the rear fenders out to accomodate the duals.

    Therein lies the question. This is my first custom project, my first MIG experience (just got a HH175) and I have very little experience with bodywork....but I have plenty of enthusiasm and drive (not to mention a very understanding fiance'.) I've done some research towards the best methods of the cab stretch, and had basically decided on cutting the back of the cab off, flanging both sides of the gap, filling the gap with sheetmetal and fabricating braces for the stretched area. However, I've recently read that there might be some problems associated with flange welds on body panels. One bodywork expert's website suggests staying away from flange welds if possible, because "...the area with double thickness will be stronger than the metal around it, and sometimes these areas will expand and contract at a different rate than the adjacent single-thickness metal, so the edges of your patch may become visible on a hot day."

    He DOES go on to suggest that "...there are times when you WOULD use an overlapped joint, such as when you are replacing an entire panel, like a complete roof or quarter panel."

    I know this question might be better asked on a bodywork forum, but after reading the posts in both, I think I'm a little more confident in the experiences in the group here. So...considering my lack of experience in this arena, what would YOU suggest I do? Have any of you had problems with flange welds later down the road? I believe the Studebaker has 18-gauge sheetmetal, so it's plenty thick to minimize warping, but what do you think?


    In the making:
    '51 Studebaker Ext. Cab 1-ton dually

  • #2
    Having just finished some floor repair work on my jeep I maybe can shed a little light on your project.

    Butt welding is a fine way to join the panels but requires more fitment work to get the new panel to butt properly to the old panels. it can be difficult to get the new panel to fit exactly butting the old sheetmetal all the way around the seam properly so that it can be welded well. also it's more likely you'd burn through (single thickness metal vs overlapped with a flange joint)

    the flanges can make filling a gap easier. The question is whether the flange on the old metal will be deep enough to allow the new sheet to fit in seamlessly once the welds are ground down.

    both require additional work. butt welding takes more work to fit it in, but I would think that it would be easier to 'finish' the seams, where as flanges would make welding etc extra but will take more post weld work to seamlessly mesh in.


    • #3
      right now i have been replacing the floor pans on my 74 Volkswagen super beetle and im doing a butt weld with it.
      the reson i chose to do a butt weld is that with a lap weld there is more of a chance of it rusting out again due to moisture being traped in bettwen the pannels.
      it is alot of work, but i think it makes for a more profesional job.



      • #4
        flange vs butt welds

        I am in the auto restoration buisness and primarily work on high end 356 porshes which are unibody cars and are always in need of just about everything from floor to roof.I am an apprentice to a guy who is one of the best in the 356 world and I am learning really fast why flange\overlap is not your friend.Overlapping gives moisture a place to live and start rusting rapidly.We butt weld everything that we replace;often the work that we do is re-do of previous bad work.Butt welding may require more preparation of your replacment part ,but My advice is to invest your time now rather then more time and money in re-do sooner then later.
        If you would like to see some real examples of the cars that I have had my experience with and the results of their time with us,check out our [email protected]
        Good luck!
        tony 007


        • #5
          Mr Studee man-

          you are not the only guy that like them.I have had a couple of these.


          • #6
            flange vs butt welds

            While it will take longer to do, butt welds will work best in the long run, as you stated with a flanged weld you will see a seam line where the panels are joined on a hot sunny day (replacement panels have flanges but are usually done so as they are hidden in a body line to make them less noticeable)as Tony mentioned if not sealed well they are prone to rusting, and with a flange weld it is very hard to do any hammer and dolly work and on this project you will become very familiar with a hammer and dolly (sorry not trying to scare you off) so take the extra time to butt weld any body panel. Here is some tips I've learned over time >to fill any small holes or gaps while mig welding, back up the hole with a piece of copper, it will hold the arc but the weld will not stick to it. >to keep the warpage to a minimum use spot welds,jumping all around the pannel to spread the heat,some suggest when the spot welds are within an inch or so of each other you can go ahead and stich them in, I would suggest you stick to the spot welds until the pannel is fully welded, very time consuming but will cause less warpage (go slow this is not something you want to rush thru)
            > and last but not least, after everything is welded up and it comes time to drag out the grinder, take it easy here also, you can warp a pannel just as easy grinding the welds down as you can by getting to carried away while welding!!
            Hope this helps


            • #7
              Just wanted to say thanks to all. Everyone had great advice. I really want to do this one right, but I guess I wasn't fully aware of the differences...I am now. I thought there would be little chance of rust in a flange once it was welded up (and in the case of floorpans, coated with undercoating). However, I'll start practicing on my welding and attempt to do butt welds...and I know where to go for advice. I'll keep you all informed of the progress.

              In the making:
              '51 Studebaker Ext. Cab 1-ton dually